In recent several years, more and more experts pay much attention to research and development on mechanical characteristic monitoring of a circuit breaker. The dynamic characteristics of a circuit breaker can reflect the running failure of the circuit breaker effectively. Therefore, the mechanical characteristic is considered as one of the most important features for a circuit breaker, and there is a requirement to monitor the mechanical characteristic of a circuit breaker.
Currently, mechanical characteristic monitoring of a circuit breaker is usually taken in an off-line environment by means of electronic sensors. The off-line environment may be a testing environment in which the circuit breaker is not electrically connected to the grid and thus would not subject the high voltage in the grid. The voltage for testing in the testing environment is relative low such that it would not impact the normal operation of the electronic sensors. However, since the circuit contact in off-line or testing environment does not subject the real high voltage, the monitored result can not accurately reflect the practical operation condition of the circuit breaker and thus can only act as a limited reference for studying the circuit breaker.
As the smart grid technology develops, there is a demand for intelligent circuit breakers which can on-line monitor the mechanical characteristic of the circuit breakers in their normal operation condition so as to support the functions of the smart grid. On-line monitoring can reflect the real operation condition of the circuit breaker, and thus is more useful in studying and controlling the circuit breaker.
An accurate monitoring to the mechanical character of a circuit breaker depends on the finding of the accurate closing and opening time point of the circuit breaker. Once the closing and opening time point is obtained, other mechanical characters of the circuit breaker, such as the contact opening gap, the contact spring stroke and the closing and opening speed can also be obtained based on the closing and opening time point in a known way.
However, the current off-line monitoring method is not suitable for on-line monitoring. The high voltage of the grid in the on-line environment can easily damage the electronics for the off-line monitoring.
In addition, since the electrical closing and opening time point under the high voltage cannot represent the real mechanical closing and opening of the movable contact due to the breakdown conducting under high voltage, it is necessary to find the mechanical closing and opening time point of the movable contact in the operation condition of the circuit breaker so as to accurately monitoring the mechanical characters of the circuit breaker. However, it is difficult to directly monitor the accurate mechanical closing and opening time point of a circuit breaker under the high voltage.
Therefore, a method for on-line monitoring the mechanical characteristic of a circuit breaker, particularly for on-line monitoring the accurate mechanical closing and opening time point is required.